Bleach is old tech and no longer works with todays sophisticated testing. Most labs now perform integrity checks on the sample prior to the actual toxin check. Many of these integrity checks now include testing for the presence of bleach. This is done with dipsticks similar to the ones found here:
http://www.meditests.com/drugadtes.html

Why not substitute with a clean sample from a freind, or a family member? Even children of stoner aquaintances make excellent sub donors. If you are brave enough to sneak in some bleach, then you certainly are brave enough to sneak in a substituted sample.